Add license to PyPI classifiers

[WilliamRoyNelson]

Adds PyPI project classifiers
Classifiers are used to add information to the classifiers panel in PyPI. Example from NumPy:

The reason that it is very important for this information to be present is that in an enterprise environment, security tools like Sonatype Nexus IQ are used to manage open source software risk. Nexus IQ specifically can be configured to classify packages according to their license. This prevents developers from inadvertently using licenses like GNU General Public License v2.0 without realizing that they may be legally obligated to make their entire project open source.

My understanding is that Nexus IQ uses the classifiers panel to determine a project's license.
Because chroma-hnswlib does not currently have a classifiers panel, Nexus cannot determine the license and treats it as a high-risk package.

By adding classifiers, chroma-hnswlib will have increased availability within enterprise environments.

[WilliamRoyNelson]

If you want, this might be a good time to do other maintenance on the setup.py file.
https://packaging.python.org/en/latest/guides/making-a-pypi-friendly-readme/#including-your-readme-in-your-package-s-metadata

I'll try to test some things out on TestPyPI over the weekend, and if this PR hasn't been merged, I'll add some more commits.